Are there any "four-in-one" creatures in the water? The strange-looking Zhang's unicorn shrimp

Recently, the international journal "Contemporary Biology" published online a paper by a Chinese and British paleontological team, which revised the appearance of the 520 million-year-old Zhang's unicorn shrimp, especially the head, which was composed of 6 parts. This new understanding not only activated the academic debate in the field of paleontology, but also provided a scientific basis for re-evaluating the evolutionary significance of this special animal fossil.

Zhang's unicorn shrimp after modeling. Source: Xinhua News Agency

The difference between the front and back is obvious: the head is divided into six parts

In 2020, Chinese scholars discovered a new species of Zhang's kylin shrimp in the Chengjiang Biota in Yunnan. Due to its unique morphology, it has five eyes at the front of its head similar to those of the Opabinia sea scorpion, and its characteristics are between true arthropods and anomalocaris. It is called a "four-in-one" animal and has unique and important significance in evolution.

The new results, based on micro-CT, computer 3D modeling and virtual anatomy, have made the fossils of more than 500 million years old vivid in a three-dimensional form, thus obtaining unexpected surprises in the study of soft body morphology. The discovery of the head eyes is particularly eye-catching. It was originally thought that Zhang's unicorn shrimp had 5 eyes, including a pair of front eyes and 3 posterior eyes, but the latest research found that Zhang's unicorn shrimp only has one middle eye and a pair of lateral eyes, a total of 3 eyes. The structure originally identified as the middle posterior eye is actually the "front bone piece".

The understanding of the appendages is also significantly different from the previous reports. In the previous reports, only two pairs of single-branched postoral appendages were found, but now it is known that the first four pairs of postoral appendages are all located on the head and are all double-branched.

Thanks to the almost complete preservation of the fossil material, the researchers were able to image the head of the unicorn shrimp and identify six parts: the front part has eyes, the second part has a pair of large grasping limbs, and the other four parts each have a pair of articulated limbs. Therefore, the morphological and quantitative descriptions of the front appendages, trunk segments, tail appendages and other parts of the Zhang's unicorn shrimp have been improved and revised. This series of new discoveries has laid an important foundation for re-evaluating the morphological characteristics, structural functions and relationship with other groups of the Zhang's unicorn shrimp, as well as its position in phylogenetic evolution.

Chimera of multiple animal characteristics is the key to arthropod evolution

The Zhang's kirin shrimp is a very peculiar-looking fossil with three eyes on the front of its head. This is very unique and unconventional in the Chengjiang biota. Naming a species after kirin has a special meaning.

Kirin shrimp fossil. Source: People's Daily

Qilin is a mythical beast with auspicious signs in ancient Chinese mythology. Generally speaking, it has the characteristics of a dragon head, a elk body, an ox tail, and wolf hooves combined into one.

The same is true for Zhang's Kirin Shrimp. It has a skeleton, or epidermis, covering its body surface, a segmented body, and multiple segments fused into a hard head shell, as well as segmented legs, which are very obvious characteristics of true arthropods.

In addition, it also has the morphology of an arthropod ancestor, and has similar appendages to the contemporary Anomalocaris. Zhang's Kirin Shrimp is like the mythical Kirin, with different body characteristics of two animals growing on its body, combining the characteristics of true arthropods and arthropods. This indicates that the evolutionary position of the Kirin Shrimp may be at the root of true arthropods, between Anomalocaris and other true arthropods.

The study found that the unicorn shrimp actually has two pairs of previously undiscovered legs, which improves and corrects the previous explanation of the head structure of the genus Unicorn Shrimp, highlights the significance of head evolution, and shows that the six-part composition of the Cambrian unicorn shrimp's head is the same as the head characteristics of modern arthropods, indicating that the head structure of modern arthropods originated from the unicorn shrimp ancestor with six segments 520 million years ago.

This peculiar-looking Zhang's unicorn shrimp provides a key link in unlocking the mystery of the origin of arthropods. It is the intermediate key to the evolution of arthropods and is also considered to be another piece of evidence to prove Darwin's theory of evolution.

Technology helps: bringing new vitality to paleontological research

In recent years, paleontological research has made great progress, which is largely attributed to the use of modern advanced technology. The new progress in this study is due to technologies such as micro-CT, computer 3D modeling and virtual anatomy.

The restored image of the unicorn shrimp. Source: People's Daily

Among them, micro-CT technology allows precious fossils to avoid the embarrassment of traditional slicing and destruction of fossils, and can peek into the internal structure of fossils. The digital technology of computer 3D modeling can perform three-dimensional rotation, showing the true face of fossils 500 million years ago in all directions, thus discovering the six real components of the head of the unicorn shrimp. Virtual dissection technology clearly shows the morphology and number of the front appendages, trunk segments, tail appendages and other parts of the unicorn shrimp, laying the foundation for a comprehensive description of the unicorn shrimp.

Nowadays, new technologies are increasingly being used in paleontological research, bringing new vitality to this ancient discipline, and paleontologists are gradually getting rid of the dilemma of being unable to conduct in-depth research due to the scarcity of fossils. With the powerful means of new technologies, scientists are uncovering more and more mysteries in the history of life on Earth, providing more and more abundant knowledge for human understanding of the evolution of the Earth and the origin and evolution of life.